nfp: change flows in apps that offload ndo_setup_tc

Change the flows a bit in preparation of follow-up changes in
ndo_setup_tc args. Also, change the error code to align with the rest of
the drivers.

Signed-off-by: Jiri Pirko <jiri@mellanox.com>
Acked-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>